Adds the lasers to the multisystem framework

Description

Adds the lasers to the multisystem framework.

The lasers are now parsed as external partners and can support the Lorentz force. The parsing is splitted such that this is compatible with generic systems.

A test is added for the Lorentz force with a charged particle.

News snippet

Adds the lasers to the multisystem framework

Checklist

• I have checked that my code follows the Octopus coding standards
• I have added tests for all the new features added in this request.